Various techniques and apparatus for partial and complete anatomic joint replacement are known in the art. There are for example the techniques and apparatus described in the following listed U.S. Pat. Nos. 3,334,624; 4,487,203; 4,549,319; 4,624,673; 4,667,664; 4,703,751; 4,736,737; 4,913,137; 4,952,213; 5,108,396; and Canadian Patent 1,237,553. There are also the studies reported at: "Humeral Head Prosthetic Arthroplasty: Surgically Relevant Geometric Considerations", Franz T. Ballmer, M.D., et al., J Shoulder Elbow Surg., Vol. 2, pages 296-304, 1993; "Anatomic Determination of Humeral Head Retroversion: The Relationship of the Central Axis of the Humeral Head to the Bicipital Groove", Edward Tillett, M.D., et al., J Shoulder Elbow Surg., Vol. 2, pages 255-6, 1993; "Total Shoulder Arthroplasty: Some Considerations Related to Glenoid Surface Contact", Franz T. Ballmer, M.D., et al., J Shoulder Elbow Surg., Vol. 3, pages 299-306, 1994; "Total Shoulder Arthroplasty: Factors Influencing Prosthetic Sizing", Joseph P. Iannotti, M.D., PhD., et al., Operative Techniques in Orthopaedics, Vol. 4, No. 4, pages 198-202, October, 1994; "A New Humeral Prosthesis for the Japanese", Toru Ishibashi, M.D., et al., pages 273-276; "The Normal Glenohumeral Relationships, An Anatomical Study of One Hundred and Forty Shoulders", Joseph P. Iannotti, M.D., et al., The Journal of Bone and Joint Surgery, Vol. 74-A, No. 4, pages 491-500, April 1992; "Articular Geometry of the Glenohumeral Joint,", Louis J. Soslowsky, Ph.D., et al., Clinical Orthopaedics and Related Research, Number 285, pages 181-190, December, 1992; and, "Quantitation of In Situ Contact Areas at the Glenohumeral-Joint: A Biomechanical Study", L. J. Soslowsky, et al., Journal of Orthopaedic Research, Vol. 10, pages 524-534, 1992. No representation is intended hereby that a thorough search of all pertinent prior art has been conducted or that no more pertinent prior art than that listed here exists. Nor should any such representation be inferred.
There are eight essential variables relating to humeral arthroplasty. These include: the diameter of curvature of the prosthesis; the percentage of the sphere with this diameter that will be used as prosthetic articular surface; the superior/inferior position of the articular surface relative to the humerus; the anterior/posterior position of the articular surface relative to the humerus; the medial/lateral articular aspect of the articular surface with respect to the humerus; the antero/posterior angulation (flexion/extension) of the articular surface relative to the prosthesis; the medial/lateral angulation (varus/valgus) of the prosthesis relative to the humerus; and, the rotational alignment of the prosthetic head with respect to the humeral axis. The goal of prosthetic arthroplasty is to duplicate the normal orientation of the humeral articular surface as well as its diameter of curvature and percentage of the sphere.
At present, no prosthetic arthroplasty system either establishes the diameter of curvature or the percentages of sphere of the humeral head to be replaced or determines the relationship of the articular surface to the orthopaedic axis of the medullary canal. As a result, the surgeon must guess at these important dimensions and relationships. Furthermore, no prosthetic system has previously been proposed which assures that when the medullary canal is reamed and the humeral head cut is made, the prosthetic articular surface will wind up in a position that duplicates the normal anatomy of the articular surface. Thus the challenges of anatomic humeral arthroplasty are to: determine the diameter of curvature of the articular surface; determine the percentage of the sphere; combine prosthetic design and rigorously guided bone cuts to assure that the desired result is achieved; and, by rigorously controlling the bone, to assure the desired relationship between the reamed medullary canal and the proximal humeral bone cut that uniquely and exactly fits the prosthesis.